1. Field of the Invention
This invention relates to arcuate pre-cast concrete tunnel lining segments.
2. Background Prior Art
UK Patent Publications Nos. 2004931 and 2131514 disclose precast arcuate concrete tunnel lining segments having end faces which are spaced apart by compressible packing pieces and which are secured together in compression by locking devices. The compressible packing pieces allow a very limited movement of the end faces towards one another when the ring of segments so formed is subjected to very high loading in the ground in which the tunnel lining is laid giving some relief from stress on the segments. The relief which can be provided by this means is however totally inadequate in situations where the segments are subjected to very high loadings for example in very deep tunnels in mines and particularly where the ground or rocks through which the tunnel passes is unstable.